This invention relates a method for producing a silica filler by direct combustion of silicon powder.
Silica fillers are well known in the prior art for use as pigments, reinforcing agents and the like. Commercially-available silica and other metal oxides are often derived from burning volatile metal halides with various fuels and oxidants. A survey of such technology is contained in an article entitled "Flame-generated Fine Particles" appearing in Chemical and Engineering News, Pages 22-27 on Aug. 6, 1984. Also in other processes, electrical energy is used in forming silica powder. For example, silica can be formed in electrically induced plasmas, and silica can be formed by the reduction of sand by carbon in a electric furnace. In the latter process, silicon monoxide flows from the electrically-heated furnace and then is burned to form a silica powder product.
Silica has been formed by burning silicon powder. Pipkin, in U.S. Pat. Nos. 2,545,896 and 2,626,874 discusses the burning of silicon powder in an unsuccessful attempt to form a suitable diffusive coating on the interior of electric light bulbs. It is believed that no one successfully has burned silicon in a flame to form a commercially-desirable silica useful as, for example, a filler and in ceramics.
Other patents descriptive of the formation of SiO.sub.2 include U.S. Pat. No. 2,535,659 to Wolf; U.S. Pat. No. 3,363,981 to Butter; U.S. Pat. No. 3,672,832 to Hulm et al and U.S. Pat. No. 4,054,641 to Carman et al.
The present inventors have addressed the problem of making silica powder from silicon powder.